Oily wastewater streams are generated at many different refinery processing units and discharged to a refinery wastewater treatment system where treatment by gravity separation and dissolved air flotation generates oily solid streams. These oily solid wastes are regulated under the Resource, Conservation, and Recovery Act (RCRA) as listed hazardous wastes. Additionally, sludge from leaded product tanks, slop oil emulsion solids, and heat exchanger bundle solids are considered listed hazardous waste. These sludges as a group are typically 4-6% solids and 15-20% oil as generated. 15,000 to 20,000 gal/day are generated at a typical petroleum refinery.
Many refineries currently deliquify these wastes and either land dispose or land treat the remaining solids. However, the 1984 Amendments to RCRA required the Environmental Protection Agency (EPA) to identify and promulgate a system of pretreatment of all hazardous wastes prior to land disposal or land treatment. EPA's choice of pretreatment was required to be based on the best demonstrated available technology and was required by Congress to be in effect by Aug. 8, 1988 for petroleum refinery wastes. If EPA did not meet this deadline, the legislative "hammer" would be the automatic prohibition of land disposal for the waste in question. This prohibition would take effect May 8, 1990. Various technologies for treating listed hazardous refinery oil sludges to render them delistable or acceptable for land disposal under the RCRA landban have been suggested, but none have been found to be entirely satisfactory.
U.S. Pat. No. 4,311,561 discloses a method for extracting bitumen from tar sand wherein the tar sand and a solvent flow in one direction through a plurality of interconnected individually sealed extraction chambers with the flow of extracted bitumen and solvent counter to the flow of tar sand and solvent. The solvents identified as being useful are hexane, pentane, benzene, halogenated liquids and xylene. The amount of bitumen in the tar sand is progressively reduced from reaction chamber to reaction chamber until the final chamber where sand and solvent alone are treated with hot water to remove the solvent and then discharge pure sand.
U.S. Pat. No. 4,341,619 discloses a process for recovering carbonaceous materials from tar sands by supercritical extraction involving countercurrent flow of the tar sand and a solvent. The solvents that are disclosed as being useful include aromatic hydrocarbons, alicyclic hydrocarbons having 5-16 carbon atoms, phenols, and nitrogen-containing compounds.
U.S. Pat. No. 4,415,442 discloses a process for the separation of entrained organic fluids from gaseous streams in a coal deashing system wherein a feed consisting of solvent, soluble coal products and insoluble coal products are placed in a first separation zone. A first heavy fraction is withdrawn from the first separation zone and the pressure level is reduced by at least 100 psig to vaporize the solvent and yield the insoluble coal products in a relatively dry, powdery form referred to in the specification as "an ash concentrate". The ash concentrate and solvent are mixed with a carrier fluid, the mixing being sufficient to obtain a turbulent flow and to scrub the vaporized solvent. The scrubbing of the vaporized solvent removes entrained organic fluids from it. The mixture is then placed in a second separation zone wherein the scrubbed solvent is separated from ash concentrate. Among the solvents described as being useful are aromatic hydrocarbons (e.g., benzene, xylene), cycloparaffins (e.g., cyclohexane), open chain monoolefins having boiling points below about 310.degree. F. (e.g., butene, pentene), and open chain saturated hydrocarbons having boiling points below about 310.degree. F. (e.g., pentane, hexane, heptane).
U.S. Pat. No. 4,434,028 discloses a process for removing oil and other organic constituents from particulate, inorganic-rich mineral solids (e.g., oil-contaminated drill cuttings) using an extractant that is in a gaseous state at atmospheric pressure and ambient temperature and is converted to a liquid or supercritical fluid during the extraction process. Extractants that are described as being useful are carbon dioxide, ethane, ethylene, propane, propylene, other hydrocarbons, and the gaseous halogenated hydrocarbons such as dichlorodifluoromethane. The process involves the steps of: separating the drill cuttings from a drilling mud in a separator; slurrying the cuttings using an oil or aqueous liquid in a slurry tank; conveying the slurry to an extractor column; circulating liquefied extractant through the extractor column in contact with the drill cuttings until the desired level of oil is extracted; advancing the extractant-oil mixture from the extractor column through a pressure reduction valve to a separator-evaporator wherein the extractant-oil mixture separates into two phases, one being an extractant phase, the other being an oil-enriched phase. The extractant phase is recirculated to the extractor column. The oil-enriched phase is subjected to subsequent separations wherein the extractant is separated from the oil. Upon completion of the extraction cycle, a water piston is advanced through the extractor column to remove remaining oil and extractant from the drill cuttings. Water is then added to the clean drill cuttings to form a slurry in the extractor column which is removed and disposed of or further treated.
U.S. Pat. No. 4,450,067 discloses a process for producing low CCR maltenic fractions and high CCR asphaltenic fractions from hydrocarbonaceous residua and other heavy oils by multisolvent-distillation-induced polarity gradient extraction. The process comprises the steps of contacting two or more suitable solvents (e.g., propane-toluene) with said residua in a liquid flooded distillation column operating in a liquid continuous mode, said solvents having a high and a low boiling point with respect to one another, said higher boiling solvent having a higher relative polarity than said lower boiling solvent and each of said boiling points being sufficiently lower than that of the residua so that the solvents are distilled into high and low polarity fractions thereby forming a low CCR maltenic overhead stream and a high CCR asphaltenic bottoms stream and thereafter recovering the solvents from the overhead stream and the bottoms stream, and recycling the solvents for reuse.
The final report for EPA Contract No. 68-02-3924 which is entitled "Pilot Plant Evaluation of Critical Fluid Extractions for Environmental Applications" discloses the results of using liquified-gas solvents in a pilot plant to extract oil from steel mill scale and bleaching clay. Two systems are described: (1) use of liquid dichlorodifluoromethane to partially extract "hydrocarbon oil" from steel mill scale, and (2) use of a non-identified solvent to remove vegetable oil (triglycerides) from bleaching clay. The report states that residual oils on both steel mill wastes and bleaching clays are soluble in liquid gas solvents such as propane.
There is a need for an efficient, economical and reliable process for separating undesirable organics from solid wastes, hazardous wastes, and the like, to render the product solids delistable or acceptable for land disposal. It would be advantageous if this process was adaptable to separating extractable organic materials from other compositions wherein such extractable organic materials are intermixed with solids and water.